Good grief, I remember this term! It always puts me in mind of this poem:
There's nothing that I wouldn't do If you would be my POSSLQ You live with me and I with you, And you will be my POSSLQ. I'll be your friend and so much more; That's what a POSSLQ is for. -- Charles Osgood
PSSSLQs have had this naming problem for quite a long while too. ;-)
OK, this one, being all acronym, does need to be capitalized: POSSLQ was coined by the US Census Bureau to denote "Persons of the Opposite Sex Sharing Living Quarters". Doesn't exactly trip off the tongue, does it? "Meet James, my current POSSLQ" isn't exactly the catchiest phrase. Other options? Partner? Significant other? Lover? Boy/girlfriend? Galpal? Guypal? Boytoy?